The three-person Public Service Board is reviewing Entergy’s request to operate Vermont Yankee until 2032.

A key issue is Yankee’s impact on the environment and whether hot water released by the nuclear plant harms fish and other river life.

Yankee uses the Connecticut River to cool its reactor, releasing water back to the river at temperatures that sometimes reach 100 degrees or more. From state Rep. David Deen’s perspective as an angler, there’s no question that the plant’s thermal pollution harms river life, in particular the American shad that migrate upriver to spawn.

“Shad is an indicator species and if you are having an impact on their behavior, what other impacts are you having on the river?” he said.

Deen, a Democrat who lives in Putney, was a witness for the Connecticut River Watershed Council, which works to restore the river. He was challenged by PSB member David Coen, who pointed out that shad had returned to the river in greater numbers this year compared to last year.

“Why should I be concerned if the population is increasing?” Coen asked.

Deen replied that many more fish were making it upstream before Yankee began discharging hot water.

“In ’92, which I think they reference as one of the best years of 700,000 fish returning, 37,000 fish went over Vernon dam, the first year they ran into heated water,” he said. “Yeah, they made it, probably was a cool year for the river. But since then things have been headed downhill.” Yankee’s expert, fisheries biologist Lawrence Barnthouse, told the PSB that there aren’t enough shad swimming upstream to Vernon to make much of a difference to the overall population in the river.

“Whatever temperature discharges are coming from the plant, exposing the shad, are affecting only a very small portion of the population, only 1 to 3 percent,” he said. “Now it’s not up to me to judge how significant that is from a regulatory perspective.”

Much of the testimony focused on temperature changes and flow rates.

Experts disagreed whether the river water mixes enough below the plant to mitigate the impact of the thermal discharge.

But lawyers for Entergy and environmental groups also sparred over the form of data that Entergy provided. An expert for the Connecticut River Watershed Council testified that Entergy took river temperature data that could be evaluated with spreadsheet software and instead converted it into a format that could not be easily analyzed by computer.

The expert, Peter Shanahan, said Entergy’s tactic made his work much more difficult. He said Entergy provided 38 boxes of paper, instead of digital files.

“The real problem was that it limited what I could do because it took so long to extract the data from the files,” he said.